Conventionally, there are a lot of suggestions on catalysts used in subjecting propylene, isobutylene, TBA or MTBE to gas phase catalytic oxidation to synthesize an unsaturated aldehyde and an unsaturated carboxylic acid, and on methods of producing the same.
The majority of such catalysts have a composition containing at least molybdenum, bismuth and iron, and industrially, a molding catalyst having such a composition is used. The molding catalysts are classified into extrusion molding catalysts, supporting molding catalysts and the like depending on their molding methods. The extrusion molding catalyst is produced usually via a process of kneading and extrusion-molding particles containing a catalyst component. On the other hand, the supporting molding catalyst is produced usually via a process of allowing a powder containing a catalyst component to be supported on a support.
Regarding the extrusion molding catalyst, there are suggested, for example, a method in which silica sol and inorganic fiber are added in production, for improvement of strength (Japanese Patent Application Laid-Open (JP-A) No. 9-52053), a method in which a certain kind of cellulose derivative is added in extrusion-molding a catalyst (JP-A No. 7-16464), and the like. However, catalysts obtained by these known methods are not necessarily sufficient as industrial catalysts from the standpoints of catalyst activity and selectivity of the intended product, and the like, and there is desired further improvement.
Besides, the above-mentioned JP-A No. 9-52053 describes that a mixture or kneaded substance of a catalyst component, silica sol and inorganic fiber is preserved by leaving it at room temperature for about 6 to 20 hours under conditions not causing evaporation of moisture (preserving treatment), before molding, to improve the mechanical strength of a molded catalyst. The reason for improvement in the strength of the molded body by preserving is described that by increase in the contact time of a catalyst component with water and the like, the catalyst component is disintegrated into near primary particles, and a molded article, when molded, becomes compact. However, preserving of a mixture or kneaded substance having no definite shape is not necessarily advantageous, and control of activity is difficult in some cases. Further, sufficient selectivity of the intended product is not necessarily obtained.
JP-A No. 2000-71313, Example 4 describes a method in which a clayey material obtained by kneading an isobutylene oxidation catalyst containing molybdenum, bismuth and iron is temporarily-molded into a cylinder, which is filled in a cylinder of a piston type extrusion molding machine, and extrusion-molded. However, in this method, a temporary-molded material in the form of cylinder and the final-molded product are not preserved, therefore, activity of the resulted catalyst may be low in some cases.